1. Technical Field
The invention relates to nanotechnology. In particular, the invention relates to structures fabricated from nano-scale particles and crystals.
2. Description of Related Art
A thin film semiconductor is a semiconductor fabricated by depositing semiconductor material on a substrate using thin film techniques. In general, thin film semiconductors are divided into two main groups: inorganic thin film semiconductors and organic thin film semiconductors. The inorganic thin film semiconductors generally comprise an inorganic material having properties of a semiconductor. Examples of inorganic semiconductor materials include, but are not limited to, silicon (Si), germanium (Ge), gallium arsenide (GaAs), and various metal-oxides (e.g., zinc oxide-ZnO). Organic thin film semiconductors comprise an organic material such as a polymer, an oligomer, or similar molecules that exhibit semiconductor properties. In some instances, the organic thin film semiconductor also includes an inorganic material (e.g., an inorganic semiconductor material) suspended in a matrix of the organic material.
Among characteristics commonly associated with thin film semiconductors and devices realized therewith are an applicability to large-area substrates, an inherent mechanical flexibility, and optical transparency. In addition, thin film semiconductors are often employed where minimizing manufacturing costs is more important than device performance. For example, a principal use of thin film semiconductors is in the form of thin film transistors (TFTs) for liquid crystal display (LCD) applications (e.g., active matrix LCDs (AMLCDs) that employ TFTs to drive and control pixels of display). Since TFTs in LCDs are generally manufactured directly on a glass substrate of the display, such applications benefit from TFTs that exhibit inherent optical transparency (e.g., ZnO-based TFTs) as well as the ability to produce TFTs on large-area substrates using thin film semiconductors.
Inorganic thin film semiconductor fabrication usually involves depositing the inorganic semiconductor material on a substrate (e.g., glass, silicon wafer, etc.) using vacuum deposition. For example, vacuum deposition techniques such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and plasma enhanced chemical vapor deposition (PECVD), are often used. As well as requiring a high vacuum, many vacuum deposition techniques subject the substrate to relatively high processing temperatures (>300° C.) during deposition. The resulting inorganic thin film semiconductor typically exhibit either an amorphous structure (e.g., a-Si:H) or a polycrystalline structure (e.g., p-Si). In some instances, annealing is used to post process the deposited thin film semiconductor to improve performance characteristics of the deposited semiconductor. Annealing may include either applying additional heat or using a laser, for example. The high temperatures as well as the requirements for achieving high vacuum during vacuum deposition often limit a material choice for and an ultimate size of a substrate. For example, high temperatures can preclude the use of some plastics as a substrate material. In addition, equipment costs for providing high vacuum to process very large substrates can be prohibitive.
Organic semiconductors have been developed, in part, to overcome the need for the high vacuum and the high temperatures typically associated with inorganic thin film semiconductor fabrication. Organic semiconductors are generally deposited as a liquid or a combination of a liquid and a solid using a method such as printing (e.g., screen printing). In some cases once deposited, the organic semiconductor is cured to produce the final thin film semiconductor. By contrast to inorganic thin film semiconductors, organic semiconductors are generally fabricated using relatively low temperature processing and ambient pressures. However, while capable of being fabricated at relatively low temperatures (e.g., <150° C.) and using relatively lower cost manufacturing equipment, organic thin film semiconductors generally exhibit poor performance characteristics (e.g., very low carrier mobility) when compared to inorganic semiconductors.